Active memory data compression system and method

ABSTRACT

An integrated circuit active memory device receives task commands from a component in a host computer system that may include the active memory device. The host system includes a memory controller coupling the active memory device to a host CPU and a mass storage device. The active memory device includes a command engine issuing instructions responsive to the task commands to either an array control unit or a DRAM control unit. The instructions provided to the DRAM control unit cause data to be written to or read from a DRAM and coupled to or from either the processing elements or a host/memory interface. The processing elements execute instructions provided by the array control unit to decompress data written to the DRAM through the host/memory interface and compress data read from the DRAM through the host/memory interface.

TECHNICAL FIELD

This invention relates memory devices, and, more particularly, totechniques for efficiently transferring data to and from active memorydevices.

BACKGROUND OF THE INVENTION

A common computer processing task involves sequentially processing largenumbers of data items, such as data corresponding to each of a largenumber of pixels in an array. Processing data in this manner normallyrequires fetching each item of data from a memory device, performing amathematical or logical calculation on that data, and then returning theprocessed data to the memory device. Performing such processing tasks athigh speed is greatly facilitated by a high data bandwidth between theprocessor and the memory devices. The data bandwidth between a processorand a memory device is proportional to the width of a data path betweenthe processor and the memory device and the frequency at which the dataare clocked between the processor and the memory device. Therefore,increasing either of these parameters will increase the data bandwidthbetween the processor and memory device, and hence the rate at whichdata can be processed.

An active memory device is a memory device having its own processingresource. It is relatively easy to provide an active memory device witha wide data path, thereby achieving a high memory bandwidth.Conventional active memory devices have been provided for mainframecomputers in the form of discrete memory devices having dedicatedprocessing resources. However, it is now possible to fabricate a memorydevice, particularly a dynamic random access memory (“DRAM”) device, andone or more processors on a single integrated circuit chip. Single chipactive memories have several advantageous properties. First, the datapath between the DRAM device and the processor can be made very wide toprovide a high data bandwidth between the DRAM device and the processor.In contrast, the data path between a discrete DRAM device and aprocessor is normally limited by constraints on the size of externaldata buses. Further, because the DRAM device and the processor are onthe same chip, the speed at which data can be clocked between the DRAMdevice and the processor can be relatively high, which also maximizesdata bandwidth. The cost of an active memory fabricated on a single chipcan is also less than the cost of a discrete memory device coupled to anexternal processor.

An active memory device can be designed to operate at a very high speedby parallel processing data using a large number of processing elements(“PEs”) each of which processes a respective group of the data bits. Onetype of parallel processor is known as a single instruction, multipledata (“SIMD”) processor. In a SIMD processor, each of a large number ofPEs simultaneously receive the same instructions, but they each processseparate data. The instructions are generally provided to the PE's by asuitable device, such as a microprocessor. The advantages of SIMDprocessing are simple control, efficient use of available databandwidth, and minimal logic hardware overhead. Another parallelprocessing architecture is multiple instruction, multiple data (“MIMD”)in which a large number of processing elements process separate datausing separate instructions.

A high performance active memory device can be implemented byfabricating a large number of SIMD PEs or MIMD PEs and a DRAM on asingle chip, and coupling each of the PEs to respective groups ofcolumns of the DRAM. The instructions are provided to the PEs from anexternal device, such as a host microprocessor. The number of PE'sincluded on the chip can be very large, thereby resulting in a massivelyparallel processor capable of processing vast amounts of data.

In operation, data to be operated on by the PEs are first written to theDRAM, generally from an external source such as a disk, network orinput/output (“I/O”) device in a host computer system. In response tocommon instructions passed to all of the PEs, the PE's fetch respectivegroups of data to be operated on by the PEs, perform the operationscalled for by the instructions, and then pass data corresponding to theresults of the operations back to the DRAM. After they have been writtento the DRAM, the results data can be either coupled back to the externalsource or processed further in a subsequent operation. By operating onthe data using active memory devices, particularly active memory devicesusing SIMD PEs and MIMD PEs, the data can be processed very efficiently.If the same data were operated on by a microprocessor or other centralprocessing unit (“CPU”), it would be necessary to couple substantiallysmaller blocks of data from the memory device to the CPU for processing,and then write substantially smaller blocks of results data back to thememory device. The wider data bus and faster data transfer speeds madepossible by using an active memory instead of a conventional memoryresult in a significantly higher data bandwidth.

Although an active memory device allows much more efficient processingof data stored in memory, the processing speed of a computer systemusing active memory devices is somewhat limited by the time required totransfer operand data to the active memory for processing and the timerequired to transfer results data from the active memory after theoperand data has been processed. During such data transfer operations,active memory devices are essentially no more efficient than passivememory devices that also require data stored in the memory device to betransferred to and from an external device, such as a CPU.

There is therefore a need for a system and method for allowing data tobe more efficiently transferred between active memory devices and anexternal system.

SUMMARY OF THE INVENTION

An integrated circuit active memory device includes a memory device andan array of processing elements, such as SIMD or MIMD processingelements, coupled to the memory device. Compressed data transferredthrough a host/memory interface port are first written to the memorydevice. The processing elements then decompresses the data stored in thememory device and write the decompressed data to the memory device. Theprocessing elements also read data from the memory device, compress thedata read from the memory device, and then write the compressed data tothe memory device. The compressed data are then transferred through thehost/memory interface. Instructions are preferably provided to theprocessing elements by an array control unit, and memory commands arepreferably issued to the memory device through a memory control unit.The array control unit and the memory control unit preferably executeinstructions provided by a command engine responsive to task commandsprovided to the active memory device by a host computer system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a computer system using an active memorydevice according to one embodiment of the invention.

FIG. 2 is a memory map showing the organization of intrinsics stored ina program memory in the active memory device of FIG. 1.

FIG. 3 is a block diagram of computer system using several active memorydevices according to one embodiment of the invention.

FIG. 4 is a flow chart showing one embodiment of a procedure fortransferring data from the active memory device to a mass storage devicein the computer system of FIG. 3.

FIG. 5 is a flow chart showing one embodiment of a procedure fortransferring data from a mass storage device to active memory devices inthe computer system of FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows an active memory device 10 according to one embodiment ofthe invention. The memory device 10 is preferably a component in a hostsystem 14, which may include a memory controller 18, a host CPU 20, amass storage device 24, such as a disk drive, a bus bridge 28 coupledbetween the memory controller 18 and the mass storage device 24, andother components that have been omitted from the host system 14 shown inFIG. 1 for the purpose of brevity and clarity. For example, a network(not shown), such as a local area network (“LAN”), may be coupled to thebus bridge 28. Also, a high speed interface (not shown), such as anInfiniband or Hypertransport interface, could be coupled to the memorycontroller 18. Other variations to the host system 14 shown in FIG. 1will be apparent to one skilled in the art.

The active memory device 10 includes a first in, first out (“FIFO”)buffer 38 that receives high level task commands from the host system14, which may also include a task address. The received task commandsare buffered by the FIFO buffer 38 and passed to a command engine 40 atthe proper time and in the order in which they are received. The commandengine 40 generates respective sequences of instructions correspondingto the received task commands. These instructions are at a lower levelthan the task commands. The instructions are coupled from the commandengine 40 to either a processing element (“PE”) FIFO buffer 44 or adynamic random access memory (“DRAM”) FIFO buffer 48 depending uponwhether the commands are PE commands or DRAM commands.

If the instructions are PE instructions, they are passed to the PE FIFObuffer 44 and then from the buffer 44 to a processing array control unit(“ACU”) 50. The ACU 50 subsequently passes microinstructions to an arrayof PEs 54. The PEs 54 preferably operate as SIMD processors in which allof the PEs 54 receive and simultaneously execute the same instructions,but they may do so on different operands. However, the PEs 54 mayalternatively operate at MIMD processors or some other type ofprocessors.

If the instruction from the command engine 40 are DRAM instructions,they are passed to the DRAM FIFO buffer 48 and then to a DRAM ControlUnit (“DCU”) 60. The DCU 60 couples memory commands and addresses to aDRAM 64 to read data from and write data to the DRAM 64. In theembodiment shown in FIG. 1, there are 256 PE's 54 each of which iscoupled to receive 8 bits of data from the DRAM 64 through registerfiles 68. The register files 68 thus allow operand data to be coupledfrom the DRAM 64 to the PEs 54, and results data to be coupled from thePEs 54 to the DRAM 64. In the embodiment shown in FIG. 1, the DRAM 64stores 16 M bytes of data. However, it should be understood that thenumber of PEs 54 used in the active memory device 10 can be greater orlesser than 256, and the storage capacity of the DRAM 64 can be greateror lesser than 16 Mbytes.

The ACU 50 executes intrinsic routines each containing severalmicroinstructions responsive to the command from the FIFO buffer 44.These microinstructions are stored in a program memory 70, which ispreferably loaded at power-up or at some other time based on specificoperations that the active memory device 10 is to perform. Control andaddress (“C/A”) signals are coupled to the program memory 70 from theACU 50. A memory map 80 of the program memory 70 according to oneembodiment is shown in FIG. 2. The memory map 80 shows a large number ofintrinsics 84-1, -2, -3, -4 . . . -N, each of which is composed of oneor more microinstructions, as previously explained. Thesemicroinstructions generally include both code that is executed by theACU 50 and code that is executed by the PEs 54. The microinstructions inat least some of the intrinsics 84 cause the PEs 54 to performrespective operations on data received from the DRAM 54 through theregister files 68. The microinstructions in other of the intrinsics 84cause data to transferred from the PEs 54 to the register files 68 orfrom the register files 68 to the PEs 54. As explained in greater detailbelow, the microinstructions in other of the intrinsics 84 are involvedin the transfer of data to and from the DRAM 54.

In operation, in response to each task command from the host system 14,the command engine 40 executes respective sequences of instructionsstored in an internal program memory (not shown). The instructionsgenerally include both code that is executed by the command engine 40and PE instructions that are passed to the ACU 50. Each of the PEinstructions that are passed to the ACU 50 is generally used to addressthe program memory 70 to select the first microinstruction in anintrinsic 84 corresponding to the PE instruction. Thereafter, the ACU 50couples command and address signals to the program memory 70 tosequentially read from the program memory 70 each microinstruction inthe intrinsic 84 being executed. As mentioned above, a portion of eachmicroinstruction from the program memory 70 is executed by the PEs 54 tooperate on data received from the register files 68.

With further reference to FIG. 1, the DRAM 54 may also be accesseddirectly by the host system 14 through a host/memory interface (“HMI”)port 90. The HMI port 90 is adapted to receive a set of memory commandsthat are substantially similar to the commands of a conventional SDRAMexcept that it includes signals for performing a “handshaking” functionwith the host system 14. These commands include, for example, ACTIVE,PRECHARGE, READ, WRITE, etc. In the embodiment shown in FIG. 1, the HMIport 90 includes a 32-bit data bus and a 14-bit address bus, which iscapable of addressing 16,384 pages of 256 words. The address mappingmode is configurable to allow data to be accessed as 8, 16 or 32 bitwords. However, other memory configurations are, of course, possible.

In a typical processing task, the host system 14 passes a relativelylarge volume of data to the DRAM 64 through the HMI port 90, often fromthe mass storage device 24. The host system 14 then passes task commandsto the active memory device 10, which cause subsets of operand data tobe read from the DRAM 64 and operated on by the PEs 54. Results datagenerated from the operations performed by the PEs 54 are then writtento the DRAM 64. After all of the subsets of data have been processed bythe PE's 54, the relatively large volume of results data are read fromthe DRAM 64 and passed to the host system 14 through the HMI port 90.Also, of course, the DRAM 64 may simply be used as system memory for thehost system 14 without the PEs 54 processing any of the data stored inthe DRAM 64.

As mentioned above, the time required to transfer relatively largevolumes of data from the host system 14 to the DRAM 64 and from the DRAM64 to the host system 14 can markedly slow the operating speed of asystem using active memory devices. If the data could be transferredtrough the HMI port 90 at a more rapid rate, the operating efficiency ofthe active memory device 10 could be materially increased.

According to one embodiment of the invention, the host system 14transfers compressed data through the HMI port 90 to the DRAM 64. Thecompressed data are then transferred to the PEs 54, which execute adecompression algorithm to decompress the data. The decompressed dataare then stored in the DRAM 64 and operated on by the PEs 54, aspreviously explained. The results data are then stored in the DRAM 64.When the data stored in the DRAM 64 are to be transferred to the hostsystem 14, the data are first transferred to the PEs 54, which execute acompression algorithm to compress the data. The compressed data are thenstored in the DRAM 64 and subsequently transferred to the host system 14through the HMI port 90. By transferring only compressed data throughthe HMI port 90, the data bandwidth to and from the DRAM 64 is markedlyincreased.

The PEs 54 preferably compress and decompress the data by executingmicroinstructions stored in the program memory 70. As previouslymentioned, some of the intrinsics 84 (FIG. 2) stored in the programmemory 70, such as 84-2, cause the PEs 54 to decompress data transferredfrom the host system 14 through the HMI port 90. Other of the intrinsics84 stored in the program memory 70, such as 84-3, cause the PEs 54 tocompress data before being transferred to the host system 14 through theHMI port 90. The intrinsics 84 can compress and decompress the datausing any of a wide variety of conventional or hereinafter developedcompression algorithms.

A single active memory device 10 may be used in a computer system asshown in FIG. 1, or multiple active memory devices 10-1, 10-2 . . . 10-nmay be used as shown in FIG. 3. In the system of FIG. 3, the activememory devices 10 are coupled to the memory controller 18′, which is, inturn, coupled to the host CPU 20′. The memory controller 18′ of FIG. 3is substantially identical to the memory controller 18 of FIG. 1 exceptthat it outputs an N-bit control signal to specify which of the activememory devices 10 is to communicate with the memory controller 18′.Other components of the computer system, some of which are shown in FIG.1, have been omitted from FIG. 3 in interest of brevity and clarity. Theuse of several active memory devices 10 can substantially increase thememory bandwidth of a computer system in which they are included becausethe host system 14′ can be passing data to or from one of the activememory devices 10 while another of the active memory devices 10 isdecompressing data that has been transferred from the host system 14′ orcompressing data prior to being transferred to the host system 14′.

The operation of the computer system shown in FIG. 3 for a typical datatransfer operation will now be explained with reference to the flowchartof FIG. 4, which illustrates the execution of a “page to disk” taskcommand from the host system 14. As is well known in the art, a page todisk command is a command that transfers data stored in a block ofmemory, known as a “page,” to a storage location in a disk drive. Theoperation is entered at 100, and the host CPU 20 formulates a “page todisk” task command at 104. At 106, the host CPU 20 computes thelocations of the page to be transferred, which is designated by a DRAMaddress in the active memory devices 10. As explained below, the memorycontroller 18′ in the host system 14′ preferably accesses each of theactive memory devices 10-1, 10-2 . . . 10-n in sequence. A memory deviceindex “I” is set to the number “N” of active memory devices 10 in thesystem at 108. The host CPU 20, through the memory controller 18, thenissues the task command to the highest order active memory device 10 at110. The task command consists of a “page to disk” command and theaddress in the active memory devices 10 from where the data is to betransferred. As explained above, this address was calculated at step106. After the task command has been issued by the memory controller 18,the memory device index I is decremented at 114 and a determination ismade at 116 whether or not the previously issued task command was issuedto the first active memory device 10-1. If the task command has not yetbeen issued to the first active memory device 10-1, the operationreturns to 110 where the “page to disk” command is issued to the nextactive memory device 10. When the task command has been issued to thefirst active memory device 10-1, the operation progresses to 120 where adelay is initiated that allows the active memory devices 10 sufficienttime to complete the task corresponding to the task commands. Thus, thetask commands may be issued to the active memory devices 10 at a ratethat is faster than the active memory devices 10 can complete the task.During the time that the active memory devices 10 are processing the“page to disk” task commands at step 120, the DRAM 64 in each of theactive memory devices 10 transfer the block of data in the designatedpage to the respective array of PEs 54 through the register files 68.The PEs 54 then compress the data by executing the microcode in anintrinsic 84 stored in the program memory 70 in each of the activememory devices 10. The PEs 54 then transfer the compressed data throughthe register files 68 back to the DRAM 64.

After sufficient time has lapsed for the active memory devices 10 tocomplete the task of compressing the read data stored in the designatedpage and making the compressed data available to the HMI port 90, directmemory access (“DMA”) operations to the mass storage device 24′ areinitiated at 124. In this regard, the DMA operations may be initiated ata rate that is faster than the mass storage device 24′ can complete theoperations. The DMA operations are simply stored as a list of DMAoperations that are sequentially completed, which is detected at 126.Each DMA operation causes the compressed data stored in the DRAM 64 tobe sequentially coupled to the mass storage device 24′ through the HMIport 90 and memory controller 18′. The “page to disk” task is thencompleted at 128.

A “memory page from disk” algorithm that is the reverse of the operationshown in FIG. 4 is shown in FIG. 5. The operation is initiated at 140,and a determination is made at 144 of the number of active memorydevices 10 to which the data in the mass storage device 24 will betransferred. The memory device index I is then set to that number at144. The host CPU 20′ then issues a command at 148 that causes thedesignated compressed data stored in the mass storage device 24′ to betransferred through the memory controller 18′ and the HMI port 90 to theDRAM 64 in the highest order active memory device 10 to which data willbe transferred. The operation waits at 150 until the data have beentransferred from the mass storage device 24′. The host CPU 20′ thenissues a decompress task command to the active memory device 10 at step154. In response to the decompress task command, the DRAM 64 in theactive memory device 10 being addressed transfers the compressed datathrough the register files 68 to the array of PEs 54. The PEs 54 thendecompress the data by executing one of the intrinsics 84 stored in theprogram memory 70, and then transfer the decompressed data through theregister files 68 to the DRAM 64.

After the data from the mass storage device 24 have been downloaded tothe DRAM 64 and decompressed, the memory device index I is decrementedat 158 in a determination is made at 160 whether I=1 corresponding tothe data being transferred from the mass storage device 24 to the firstactive memory device 10-1. If not, the operation returns to 150 torepeat the process described above. If all of the data have beentransferred from the mass storage device 24, the operation branches to170 where it waits for all of the downloaded data to be decompressed bythe PEs 54 and stored in the respective DRAM 64. The operation and thentakes its through 174.

Although only the “page to disk” and the “memory page from disk”operations have been described herein, it will be understood that otheroperations can also occur, and corresponding intrinsics 84 are stored inthe program memory 70 to assist in carrying out these operations. Forexample, intrinsics 84 could be provided that cause the PEs 54 tocompress and/or decompress all of the data stored in the DRAM 64, or tocompressed and/or decompress data stored in the DRAM 64 only withincertain ranges of addresses. Other operations in which the PEs 54compress or decompress data will be apparent to one skilled in the artand, of course, can also be carried out in the active memory device 10.

From the foregoing it will be appreciated that, although specificembodiments of the invention have been described herein for purposes ofillustration, various modifications may be made without deviating fromthe spirit and scope of the invention. For example, rather than transferthe compressed data from the HMI port 90 to the DRAM 64 prior to beingdecompressed by the PEs 54, it may be possible to transfer thecompressed data directly from the HMI port 90 to the register files 68or some other component (not shown) before being decompressed by the PEs54. Similarly, rather than storing data compressed by the PEs 54 in theDRAM 64 before being transferring the compressed data through the HMIinterface 90, it may be possible to store the data compressed by the PEs54 in the register files 68 or some other location prior to beingtransferred through the HMI port 90. As another example, instead of orin addition to transferring the data from the active memory device 10 tothe mass storage device 24, it may be transferred to other components,such as the host CPU 20, a graphics processor (not shown), etc., througha DMA operation or some other operation. Furthermore, as mentionedabove, the PEs 54 need not SIMD PEs, but instead can be other types ofprocessing devices such as multiple instruction multiple data (“MIMD”)processing elements. Accordingly, the invention is not limited except asby the appended claims.

1. An integrated circuit active memory device comprising: a memorydevice having a data bus containing a plurality of data bus bits; anarray of processing elements each of which is coupled to a respectivegroup of the data bus bits, each of the processing elements having aninstruction input coupled to receive processing element instructions forcontrolling the operation of the processing elements; a host interfaceport operable to transfer data to and from the active memory device; anda control unit being operable to receive task commands and to generatecorresponding sequences of instructions responsive to each of the taskcommands to control the operation of the memory device and theprocessing elements, at least some of the instructions generated by thecontrol unit causing the processing elements to either decompress datatransferred to the active memory device through the host interface portand then store the decompressed data in the memory device or to compressdata transferred from the memory device that is to be transferred fromthe active memory device through the host interface port. 2-43.(canceled)